Vehicle combinations comprising a tractor vehicle and a towed vehicle may be equipped with electronic brake systems (EBS) which may comprise a function for regulation of coupling force (CFC, coupling force control). Said CFC function is suited to continuously controlling the distribution of braking force between brake systems of said tractor vehicle and said towed vehicle. This makes it possible for brake action to be controlled in such a way that forces acting at a coupling point between said tractor vehicle and said towed vehicle are minimized or eliminated, resulting in a so-called brake balance between the tractor vehicle and the towed vehicle. It is desirable and in some countries even legally required that both said tractor vehicle and said towed vehicle be capable of braking their own weight in any operating situation.
An existing electronic brake system comprises a first brake control unit situated on said tractor vehicle and a second brake control unit situated on said towed vehicle, said first brake control unit being a primary control unit and said second brake control unit a secondary control unit. Said first control unit performs said function for regulation of coupling force and is therefore arranged to continuously determine and control the distribution of braking force for the vehicle combination. Said second brake control unit is arranged to control brake action pertaining to said towed vehicle on the basis of said brake force distribution determined by said first brake control unit.
Said coupling force function comprises an iterative method which uses a number of parameters, e.g. the respective weights of the tractor vehicle and the towed vehicle, the prevailing acceleration or retardation of the vehicle combination, the rotation speeds of the latter's wheels etc. as a basis for determining adaptation data continuously during braking of the vehicle combination. Said adaptation data pertain both to said tractor vehicle and to said towed vehicle.
A number of braking processes of the vehicle combination are currently required for said CFC function to operate. An initial assumption for said function is a suitable braking force distribution, although this assumption may be more or less appropriate. Typically five to ten braking processes of the vehicle combination may be necessary before said function can conduct control of braking force distribution in a more appropriate way whereby forces at said coupling point between the tractor vehicle and the towed vehicle can be effectively minimized during braking processes. The fact that the vehicle combination has to go through a number of braking processes before said CFC function can determine brake action distribution in an optimum way means that said coupling point between the vehicles is subject to undesirable effects which may lead inter alia to undesirable brake wear. In the worst case said undesirable effects will lead to a non-optimum braking method, with potential consequent risk to the safety of other road users.
A driver of said vehicle combination may have problems when braking the vehicle combination before said function intervenes. He/she may find that said towed vehicle is not braked sufficiently and “pushes” the tractor vehicle. This may of course be disturbing and stressful for the driver of the vehicle combination, with potential consequent adverse effects with regard to traffic safety.
It should be noted that different towed vehicles may be coupled to a tractor vehicle. When connecting a different towed vehicle, said CFC function is suited to applying initial values for adaptation of brake action distribution. This makes it possible for said intervention process to be reliable in that a number of braking processes are required to arrive at suitable control of brake systems on both said tractor vehicle and said towed vehicle.